Overall perspective of electrospun semiconductor metal oxides as high-performance gas sensor materials for NOx detection.

Gas sensors based on nanostructured semiconductor metal oxide (SMO) materials have been extensively investigated as key components due to their advantages over other materials, namely, high sensitivity, stability, affordability, rapid response and simplicity. However, the difficulty of working at high temperatures, response in lower concentration and their selectivity are huge challenges of SMO materials for detecting gases. Therefore, researchers have not stopped their quest to develop new gas sensors based on SMOs with higher performance. This paper begins by highlighting the importance of nitrogen monoxide (NO) and nitrogen dioxide (NO2) detection for human health and addresses the challenges associated with existing methods in effectively detecting them. Subsequently, the mechanism of SMO gas sensors, analysis of their structure and fabrication techniques focusing on electrospinning technique, as well as their advantages, difficulties, and structural design challenges are discussed. Research on enhancing the sensing performance through tuning the fabrication parameters are summarized as well. Finally, the problems and potential of SMO based gas sensors to detect NOx are revealed, and the future possibilities are stated.

Bacterial Cellulose Electrospun Fiber Mesh Coated with Chitin Nanofibrils for Eardrum Repair.

In this study, we develop a bio-based and bioactive nanofibrous patch based on bacterial cellulose (BC) and chitin nanofibrils (CNs) using an ionic liquid as a solvent for BC, aimed at tympanic membrane (TM) repair. Electrospun BC nanofiber meshes were produced via electrospinning, and surface-modified with CNs using electrospray. The rheology of the BC/ionic liquid system was investigated. The obtained CN/BC meshes underwent comprehensive morphological, physicochemical, and mechanical characterization. Cytotoxicity tests were conducted using L929 mouse fibroblasts, revealing a cell viability of 97.8%. In vivo tests on rabbit skin demonstrated that the patches were nonirritating. Furthermore, the CN/BC fiber meshes were tested in vitro using human dermal keratinocytes (HaCaT cells) and human umbilical vein endothelial cells as model cells for TM perforation healing. Both cell types demonstrated successful growth on these scaffolds. The presence of CNs resulted in improved indirect antimicrobial activity of the electrospun fiber meshes. HaCaT cells exhibited an upregulated mRNA expression at 6 and 24 h of key proinflammatory cytokines crucial for the wound healing process, indicating the potential benefits of CNs in the healing response. Overall, this study presents a natural and eco-sustainable fiber mesh with great promise for applications in TM repair, leveraging the synergistic effects of BC and CNs to possibly enhance tissue regeneration and healing. Impact statement Repair of tympanic membrane perforations following chronic otitis media is a main clinical issue in otologic surgery, where the underlying infection obstacles self-healing. To address this challenge, our study proposes a bio-based patch made of nanoscale carbohydrate materials (i.e., bacterial cellulose electrospun fibers and chitin nanofibrils) processed via green solvents. The scaffold is nonirritating in vivo, and cytocompatible with fibroblasts, endothelial cells, and keratinocytes. In epithelial cells, it stimulates the expression of the antimicrobial peptide human beta defensin 2, with a pathway of cytokine expression compatible with the wound healing process. Therefore, it could be applied with unsolved infective pathology.

Nanofibers-Based Piezoelectric Energy Harvester for Self-Powered Wearable Technologies.

The demands for wearable technologies continue to grow and novel approaches for powering these devices are being enabled by the advent of new energy materials and novel manufacturing strategies. In addition, decreasing the energy consumption of portable electronic devices has created a huge demand for the development of cost-effective and environment friendly alternate energy sources. Energy harvesting materials including piezoelectric polymer with its special properties make this demand possible. Herein, we develop a flexible and lightweight nanogenerator package based on polyvinyledene fluoride (PVDF)/LiCl electrospun nanofibers. The piezoelectric performance of the developed nanogenator is investigated to evaluate effect of the thickness of the as-spun mat on the output voltage using a vibration and impact test. It is found that the output voltage increases from 1.3 V to 5 V by adding LiCl as additive into the spinning solution compared with pure PVDF. The prepared PVDF/LiCl nanogenerator is able to generate voltage and current output of 3 V and 0.5 µA with a power density output of 0.3 µW cm-2 at the frequency of 200 Hz. It is found also that the developed nanogenerator can be utilized as a sensor to measure temperature changes from 30 °C to 90 °C under static pressure. The developed electrospun temperature sensor showed sensitivity of 0.16%/°C under 100 Pa pressure and 0.06%/°C under 220 Pa pressure. The obtained results suggested the developed energy harvesting textiles have promising applications for various wearable self-powered electrical devices and systems.

Electrospun ZnO/Poly(Vinylidene Fluoride-Trifluoroethylene) Scaffolds for Lung Tissue Engineering.

Due to the morbidity and lethality of pulmonary diseases, new biomaterials and scaffolds are needed to support the regeneration of lung tissues, while ideally providing protective effects against inflammation and microbial aggression. In this study, we investigated the potential of nanocomposites of poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] incorporating zinc oxide (ZnO), in the form of electrospun fiber meshes for lung tissue engineering. We focused on their anti-inflammatory, antimicrobial, and mechanoelectrical character according to different fiber mesh textures (i.e., collected at 500 and 4000 rpm) and compositions: (0/100) and (20/80) w/w% ZnO/P(VDF-TrFE), plain and composite, respectively. The scaffolds were characterized in terms of morphological, physicochemical, mechanical, and piezoelectric properties, as well as biological response of A549 alveolar epithelial cells in presence of lung-infecting bacteria. By virtue of ZnO, the composite scaffolds showed a strong anti-inflammatory response in A549 cells, as demonstrated by a significant decrease of interleukin (IL) IL-1α, IL-6, and IL-8 expression in 6 h. In all the scaffold types, but remarkably in the aligned composite ones, transforming growth factor ß (TGF-ß) and the antimicrobial peptide human ß defensin-2 (HBD-2) were significantly increased. The ZnO/P(VDF-TrFE) electrospun fiber meshes hindered the biofilm formation by Staphylococcus aureus and Pseudomonas aeruginosa and the cell/scaffold constructs were able to impede S. aureus adhesion and S. aureus and P. aeruginosa invasiveness, independent of the scaffold type. The data obtained suggested that the composite scaffolds showed potential for tunable mechanical properties, in the range of alveolar walls and fibers. Finally, we also showed good piezoelectricity, which is a feature found in elastic and collagen fibers, the main extracellular matrix molecules in lungs. The combination of all these properties makes ZnO/P(VDF-TrFE) fiber meshes promising for lung repair and regeneration. Impact statement Airway tissue engineering is still a major challenge and an optimally designed scaffold for this application should fulfill a number of key requirements. To help lung repair and regeneration, this study proposes a nondegradable scaffold, with potential for tuning mechanical properties. This scaffold possesses a strong anti-inflammatory character, and is able to hinder microbial infections, sustain epithelial cell growth, and provide physiological signals, like piezoelectricity. The development of such a device could help the treatment of pulmonary deficiency, including the ones induced by inflammatory phenomena, primary and secondary to pathogen infections.

Ligand & band gap engineering: tailoring the protocol synthesis for achieving high-quality CsPbI3 quantum dots.

Hot-injection has become the most widespread method used for the synthesis of perovskite quantum dots (QDs) with enormous interest for application in optoelectronic devices. However, there are some aspects of the chemistry involved in this synthesis that have not been completely investigated. In this work, we synthesized ultra-high stable CsPbI3 QDs for more than 15 months by controlling two main parameters: synthesis temperature and the concentration of capping ligands. By increasing the capping ligand concentration during the QD synthesis, we were able to grow CsPbI3 in a broad range of temperatures, improving the photophysical properties of QDs by increasing the synthesis temperature. We achieved the maximum photoluminescence quantum yield (PLQY) of 93% for a synthesis conducted at 185 °C, establishing an efficient surface passivation to decrease the density of non-radiative recombination sites. Under these optimized synthesis conditions, deep red LEDs with an External Quantum Efficiency (EQE) higher than 6% were achieved. The performance of these LEDs is higher than that of the reported CsPbI3 QD-LEDs containing standard capping agents, without additional elements or further element exchange. We show that it is possible to produce stable CsPbI3 QDs with high PLQY and red emission beyond the requirement of the Rec. 2020 standards for red color.

Feasibility of Using Vitamin E-Loaded Poly(ε-caprolactone)/Gelatin Nanofibrous Mat to Prevent Oxidative Stress in Skin.

Some occupational skin exposures lead to the formation of reactive oxygen species (ROS). The occupational exposure of workers to ROS has been found to be associated with an increased risk of developing skin injuries; therefore, it is essential to protect skin against ROS formation. Recently, some studies have been conducted on introducing better alternatives for skin protection. Nanofibers are good candidates for this purpose. The current study was carried out to assess vitamin E-loaded hybrid Poly(ε-caprolactone) (PCL)/gelatin (Gt) nanofibres mats as protective layers of skin exposed to occupational exposures. Vitamin E (VE) was successfully incorporated into PCL/Gt nanofibers while they were formed by electrospinning method. Nanofibers mats were characterized using scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR). Their degradation behavior, in vitro release, biocompatibility, and antioxidant activity were studied. The diameters of the PCL/Gt/VE nanofibers decreased with the addition of vitamin E. The degradation rate of nanofibers was equal to 42.98 and 50.69% during 7 and 14 days, respectively. Nanofibers containing vitamin E showed an initial burst followed by a sustained release. The PCL/Gt/VE nanofibers exhibited good free radical scavenging activities despite being exposed to a high electrical potential during electrospinning. PCL/Gt/VE nanofibers supported a higher level of viability compared to PCL/Gt ones and significantly assisted human skin cells against tert-Butyl hydroperoxide (t-BHP) induced oxidative stress. Overall, PCL/Gt/VE nanofibers can potentially be used to protect skin against oxidative stress as a novel approach for worker's healthcare.

Potential core-shell designed scaffolds with a gelatin-based shell in achieving controllable release rates of proteins for tissue engineering approaches.

The biomaterials design as core-shell structures opens a new door to the release of susceptible biomolecules in a controllable manner and enables to place natural biomaterials as shell layers to impart the effective biofunctional features at surfaces. In this study, core-shell designed scaffolds were prepared using coaxial electrospinning with hybrid of gelatin (GT)/polycaprolactone (PCL) at different weight ratios as their shell and protein solution as their core, followed by cross-linking to impart controllable release rates, tunable mechanical properties, and enhanced cytocompatibility. SEM, FM, and TEM confirmed the successful production of uniform core-shell nanofibers and homogeneous protein distribution. Results showed that an increase in GT proportion in the shell resulted in a decrease in fiber diameter, an increase of Young's modulus, and an intense burst release of BSA 0.2% which could be controlled through cross-linking. The mechanical tests revealed that the GT/PCL combining and cross-linking improved mechanical properties which correlated with an increase in spreading and proliferation of HUVECs. A slight burst release was also detected from BSA 0.05% and EGF encapsulated GT73P-cross-linked scaffold which demonstrated their applicability for a controlled release of dilute proteins. We were able to successfully incorporate two types of protein with different concentrations without supporting polymer into the GT shell to provide scaffolds possessing tunable mechanical properties and controllable release rates through blending with PCL at different ratios and/or cross-linking. These findings are promising to promote delivery systems of angiogenic growth factors that are needed a sustained release with different rates at each angiogenesis stage. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2019.

Flexible hybrid structure piezoelectric nanogenerator based on ZnO nanorod/PVDF nanofibers with improved output.

This study aimed to develop a novel hybrid piezoelectric structure based on poly(vinylidene difluoride) nanofibers (PVDF NFs) and zinc oxide nanorods (ZnO NRs) which eliminate the need for post poling treatment in such hybrid structures. Mechanism of electrical performance enhancement of the hybrid structure is also discussed in this paper. To study the effect of hybridization on piezoelectric performance, pristine ZnO NRs and pristine PVDF NF nanogenerators were also fabricated. The piezoelectric performance of these three nanogenerators was evaluated under periodic deformation at low frequency. The output power of the hybrid structure was found to be enhanced compared to pristine ZnO NRs and PVDF NFs nanogenerators. Such simple hybrid devices that do not need to complicated post poling treatment are more efficient than previous hybrid PVDF/ZnO nanogenerators for practical application. This improved piezoelectric nanogenerator is expected to enable various applications in the field of self-powered devices and wearable energy harvesting to harvest mechanical energy from the human activities.

Crystal polymorphism in polydiacetylene-embedded electrospun polyvinylidene fluoride nanofibers.

In this study, polydiacetylene (PDA) is embedded in electrospun polyvinylidene fluoride (PVDF) nanofibers for the preparation of mats with dual colorimetric and piezoelectric responses. The diacetylene monomers are self-assembled during the electrospinning process. The PDA-embedded PVDF nanofibers in the blue phase are obtained via photo-polymerization upon UV-light irradiation. The colorimetric transition of the nanofibers is studied as a function of temperature using a spectrophotometer. The morphology and crystal polymorphism of the nanofibers are investigated. The results show that the addition of PDA increases the diameter of the nanofibers due to the increase in the electrospinning solution viscosity. The results of Fourier transform infrared and wide angle X-ray diffraction demonstrate that PDA has the effect of inhibiting the growth of non-polar α-phase crystals, while promoting the growth of the polar ß-phase. However, the red phase of PDA-embedded PVDF exhibits a lower intensity of the ß-phase in comparison to that of the blue phase. In fact, the blue-to-red color transition of the PDA-embedded electrospun PVDF nanofibers is accompanied by the variation of piezoelectric signaling caused by variations in the ß-phase. This phenomenon creates great potential in commercial detection sensors in addition to their colorimetric detection properties.

Optimization of electrospinning parameters for polyacrylonitrile-MgO nanofibers applied in air filtration.

UNLABELLED: The present study aimed to optimize the electrospinning parameters for polyacrylonitrile (PAN) nanofibers containing MgO nanoparticle to obtain the appropriate fiber diameter and mat porosity to be applied in air filtration. Optimization of applied voltage, solution concentration, and spinning distance was performed using response surface methodology. In total, 15 trials were done according to the prepared study design. Fiber diameter and porosity were measured using scanning electron microscopic (SEM) image analysis. For air filtration testing, the nanofiber mat was produced based on the suggested optimum conditions for electrospinning. According to the results, the lower solution concentration favored the thinner fiber. The larger diameter gave a higher porosity. At a given spinning distance, there was a negative correlation between fiber diameter and applied voltage. Moreover, there were curvilinear relationships between porosity and both spinning distance and applied voltage at any concentration. It was also concluded that the developed filter medium could be comparable to the high-efficiency particulate air (HEPA) filter in terms of collection efficiency and pressure drop. The empirical models presented in this study can provide an orientation to the subsequent experiments to form uniform and continuous nanofibers for future application in air purification. IMPLICATIONS: High-efficiency filtration is becoming more important, due to decreasing trends air quality. Effective filter media are increasingly needed in industries applying clean-air technologies, and the necessity for developing the high-performance air filters has been more and more felt. Nanofibrous filter media that are mostly fabricated via electrospinning technique have attracted considerable attention in the last decade. The present study aimed to develop the electrospun PAN-containing MgO nanoparticle (using the special functionalities such as absorption and adsorption characteristics, antibacterial functionality, and as a pore-forming agent) filter medium through experimental investigations for application in high-performance air filters.

Electrospinning of chitosan/sericin/PVA nanofibers incorporated with in situ synthesis of nano silver.

Here, chitosan/sericin/poly(vinyl alcohol) as a biodegradable nanofibrous membrane was prepared through electrospinning with and without silver nitrate. The influences of spinning conditions including volume ratio of chitosan and sericin, voltage and spinning distance at constant feed rate on the fiber morphology and size distribution were examined by SEM and Image J software. The FT-IR spectrum and EDAX were used to indicate the chemical structure of nanofibrous membrane. In addition, the effect of AgNO3 on the nanofibers diameter and its antibacterial activity was investigated. The optimum conditions obtained with chitosan:sericin (50:50, v/v), 22 kV voltage, 10 cm spinning distance at 0.25 mL/h feed rate to prepare nanofibers with small diameter and narrow size distribution without beads. The mean diameter of nanofibers was about 180 nm while introducing AgNO3 led to smaller nanofibers diameter about 95 nm. Moreover, the presence of AgNO3 produced an excellent antibacterial activity against Escherchia coli.

Drug release profile in core-shell nanofibrous structures: a study on Peppas equation and artificial neural network modeling.

Release profile of drug constituent encapsulated in electrospun core-shell nanofibrous mats was modeled by Peppas equation and artificial neural network. Core-shell fibers were fabricated by co-axial electrospinning process using tetracycline hydrochloride (TCH) as the core and poly(l-lactide-co-glycolide) (PLGA) or polycaprolactone (PCL) as the shell materials. The density and hydrophilicity of the shell polymers, feed rates and concentrations of core and shell phases, the contribution of TCH in core material and electrical field were the parameters fed to the perceptron network to predict Peppas constants in order to derive release pattern. This study demonstrated the viability of the prediction tool in determining drug release profile of electrospun core-shell nanofibrous scaffolds.

Three-dimensional pore structure analysis of polycaprolactone nano-microfibrous scaffolds using theoretical and experimental approaches.

In this article the pore structure and porosity parameters of polycaprolactone (PCL) nano-microfibrous scaffolds are investigated using a predicting theoretical model and a nondestructive evaluation approach based on confocal laser scanning microscopy (CLSM) and three-dimensional image analysis. Different fibrous scaffolds with different fiber diameters produced by electrospinning process and their 3D-pore structure were evaluated theoretically and also compared to results of CLSM and capillary flow porometery methods. The effect of polymer concentration on the pore structure of scaffolds was also investigated. The results showed that, the introduced approach not only can measure the pore size distribution of nanofibrous scaffolds, but also can measure pore interconnectivity of fibrous scaffolds. Furthermore, the results showed that increasing the fiber diameter resulted from increasing the polymer concentration in solvent can effectively increase the pore dimensions within the scaffold structure.

The influence of surface nanoroughness of electrospun PLGA nanofibrous scaffold on nerve cell adhesion and proliferation.

Electrospun nanofibrous scaffolds in neural tissue engineering provide an alternative approach for neural regeneration. Since the topography of a surface affects the microscopic behaviour of material; the creation of nanoscale surface features, which mimic the natural roughness of live tissue, on polymer surfaces can promote an appropriate cell growth and proliferation. In this research, a unique PLGA nanofibrous structure was fabricated without any post-electrospinning treatment. Scaffolds were prepared in two general groups: cylindrical and ribbon-shaped electrospun fibres, with smooth and rough (porous and grooved) surfaces. The experiments about nerve cell culture have demonstrated that the nanoroughness of PLGA electrospun scaffolds can increase the cell growing rate to 50 % in comparison with smooth and conventional electrospun scaffolds. SEM and AFM images and MTT assay results have shown that the roughened cylindrical scaffolds enhance the nerve growth and proliferation compared to smooth and ribbon-shaped nanofibrous scaffolds. A linear interaction has been found between cell proliferation and surface features. This helps to approximate MTT assay results by roughness parameters.

A theoretical analysis and prediction of pore size and pore size distribution in electrospun multilayer nanofibrous materials.

Electrospinning process can fabricate nanomaterials with unique nanostructures for potential biomedical and environmental applications. However, the prediction and, consequently, the control of the porous structure of these materials has been impractical due to the complexity of the electrospinning process. In this research, a theoretical model for characterizing the porous structure of the electrospun nanofibrous network has been developed by combining the stochastic and stereological probability approaches. From consideration of number of fiber-to-fiber contacts in an electrospun nanofibrous assembly, geometrical and statistical theory relating morphological and structural parameters of the network to the characteristic dimensions of interfibers pores is provided. It has been shown that these properties are strongly influenced by the fiber diameter, porosity, and thickness of assembly. It is also demonstrated that at a given network porosity, increasing fiber diameter and thickness of the network reduces the characteristic dimensions of pores. It is also discussed that the role of fiber diameter and number of the layer in the assembly is dominant in controlling the pore size distribution of the networks. The theory has been validated experimentally and results compared with the existing theory to predict the pore size distribution of nanofiber mats. It is believed that the presented theory for estimation of pore size distribution is more realistic and useful for further studies of multilayer random nanofibrous assemblies.

Three-dimensional pore structure analysis of nano/microfibrous scaffolds using confocal laser scanning microscopy.

Specific internal pore architectures are required to provide the needed biological and biophysical functions for fibrous scaffolds as these architectures are critical to cell infiltration and in-grows performance. However, the key challenging on evaluating 3D pore structure of fibrous scaffolds for better understanding the capability of different structures for biological application is not well investigated. This article reports a fast, accurate, nondestructive, and comprehensive evaluation approach based on confocal laser scanning microscopy (CLSM) and three-dimensional image analysis to study the pore structure and porosity parameters of Nano/Microfibrous scaffolds. Also a new method of making the fiber fluorescent using quantum dots (QDs) was applied before 3D imaging. Fibrous scaffolds with different porosity parameters produced by electrospinning and their 3D-pore structure was evaluated by this approach and the results were compared to results of capillary flow porometry. The pore structural properties measured in this approach are in good agreement with that measured by the capillary flow porometry (with significant level 0.05). Furthermore, the introduced approach can measure the pore interconnectivity of the scaffold.